Advanced technological uses for wire and cable have imposed many new requirements upon traditional wire and cable specifications and functions. In missile and aerospace environments, for example, the need for lighter weight cabling is directly related to aircraft performance and operating cost. Also, wiring is often required to meet stringent shielding specifications, since it is contemplated that the missile or aircraft will have to fly through radiation and electrical interference fields without compromising the on-board electronics.
Presently, wire and cables are shielded electrically by braiding wire mesh shields about the primary wire core and insulation. This shielding is meant to prevent RFI and EMI disturbances from influencing the signals in the cable.
As the advanced technology requirements impose greater stringency in shielding and weight specifications, these previously functional braided articles become unacceptable. Shielding leakages occur in these conventional cables by virtue of the looseness by which the wire mesh is braided leaving holes in the shield web. In addition, the stiffness of the metal wire used in braiding makes it difficult to conform the mesh to the insulation core surfaces, leaving small gaps. Such gaps limit the frequency range in which the cable or wire can be operationally effective. While it may be possible to use finer wire mesh to resolve some of the above-mentioned shielding problems, it is still necessary to contend with the lower weight requirements that these environments impose. The lower weight requirements cannot be practically met by using wire mesh braiding techniques.
The present invention has resolved the aforementioned problems by the development of a new type of shielded wire and cable article. The new article of this invention contemplates the use of shielding composed of fine mesh yarns or fibers that have been metallically coated with an extremely thin layer of material. The metallic layer is coated upon the fibers in thin layers. The yarns contemplated for use in the invention have high tensile strength and flexibility, in which nylon, Kevlar, or carbon fibers have proven acceptable.
The high tensile strength and flexibility of the fibers of this invention ensures that the fibers can be made thin without losing structural integrity. The thinner the fiber, the tighter it can be braided or woven; and hence, the greater the shielding effectiveness. Also, the greater flexibility of the fiber mesh, as compared to wire mesh, provides a greater conformity to the surface of the underlying insulation. Such improved conformity further improves the closeness and tightness of the mesh shield. This also contributes to a higher shielding frequency range capability.
The fibers have a clear weight advantage over that of metallic wire, providing the solution to the most vexing aspect of the new aerospace specifications.